The quantity \(\alpha \equiv ({g^{\prime 2} Z^2})({Z_1}/{A_1} - {Z_2}/{A_2})/({G A^2 u^2})\)  bounded from above as a function of the interaction range \(\lambda \equiv 1/M_{Z^{\prime }}\)  [1]}. The current limit on \(g^{\prime }\)  is shown by the cyan shaded region (excluded) in Fig. REF .
